A high performance matrix-assisted laser desorption ionization (MALDI) time-of-light (TOF) mass spectrometer is requested, to be located in the University of California, Davis central mass spectrometry/protein sequencing laboratory. The principal investigator and eleven major users of the proposed instrument are all NIH funded investigators involved in research that requires the capabilities of such a mass spectrometer in order to solve problems in large molecule characterization that have arisen in the course of their work. These users study such health-related issues as health effects of agrochemicals, pulmonary effects of oxidative pollutants, protein modification in the lung, primary biliary cirrhosis, reproductive toxicology, copper nutrition, and monocrotaline-induced pulmonary hypertension. Users wish to use the proposed instrument to identify proteins isolated in small quantities by gel electrophoresis; to determine the location and identify of post-translational modifications of proteins; to determine the location of reactive residues in the active sites of enzymes and receptors: to assess the purity and homogeneity of proteins prior to crystallization and further processing; to characterize large porphyrin arrays; and to perform a variety of other tasks. Many of the users NIH funded projects will be facilitated by the capabilities of a high performance MALDI/TOF mass spectrometer.